Methods and apparatus for enabling distributed frequency synchronization

ABSTRACT

A method, an apparatus, and a computer program product for wireless communication are provided in connection with enabling distributed frequency synchronization based on an average clock rate. In one example, a UE is equipped to receive a synchronization signal from each of one or more UEs, perform an averaging process to generate an average clock rate based at least on the received synchronization signals, and adjust an internal clock rate based on the average clock rate. In another example, a UE is equipped to adjust an internal clock rate of a UE based on timing information provided by a GPS, select a sequence to communicate a synchronization signal transmission from a subset of sequences reserved for GPS connected UEs, and transmit the synchronization signal based on the adjusted internal clock rate.

BACKGROUND

1. Field

The present disclosure relates generally to communication systems, andmore particularly, to enabling distributed frequency synchronizationbased on an average clock rate as part of device to device (D2D)communications in a wireless wide area network (WWAN).

2. Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency division multiple access (SC-FDMA) systems, andtime division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of a telecommunicationstandard is Long Term Evolution (LTE). LTE is a set of enhancements tothe Universal Mobile Telecommunications System (UMTS) mobile standardpromulgated by Third Generation Partnership Project (3GPP). LTE isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lower costs, improve services, make use of newspectrum, and better integrate with other open standards using OFDMA onthe downlink (DL), SC-FDMA on the uplink (UL), and multiple-inputmultiple-output (MIMO) antenna technology. LTE may support directdevice-to-device (peer-to-peer) communication (e.g., LTE-Direct).

Currently, an aspect of supporting device to device (D2D) communicationsin an LTE environment (e.g., LTE-Direct) is D2D synchronization. D2Dsynchronization may include timing synchronization and frequencysynchronization. Where a D2D communications are supported without acentralized controlling entity, D2D synchronization may be performed ina distributed manner (e.g., amount devices in the network). Distributedfrequency synchronization is needed to enable a communication systemwhich works without an infra-structure (e.g., no central controllingentity).

As the demand for D2D communication increases, there exists a need formethods/apparatuses for enabling user equipments (UEs) to performdistributed frequency synchronization for supporting D2D communicationwithin an LTE environment.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In accordance with one or more aspects and corresponding disclosurethereof, various aspects are described in connection with enablingdistributed frequency synchronization based on an average clock rate. Inone example, a UE is equipped to receive a synchronization signal fromeach of one or more UEs, perform an averaging process to generate anaverage clock rate based at least on the received synchronizationsignals, and adjust an internal clock rate based on the average clockrate. In another example, a UE is equipped to adjust an internal clockrate of a UE based on timing information provided by a globalpositioning system (GPS), select a sequence to communicate asynchronization signal transmission from a subset of sequences reservedfor GPS connected UEs, and transmit the synchronization signal based onthe adjusted internal clock rate.

According to related aspects, a method for enabling distributedfrequency synchronization based on an average clock rate is provided.The method can include receiving, by a UE, a synchronization signal fromeach of one or more UEs. Further, the method can include performing anaveraging process to generate an average clock rate based at least onthe received synchronization signals. Moreover, the method may includeadjusting an internal clock rate based on the average clock rate.

Another aspect relates to a communications apparatus for enablingdistributed frequency synchronization based on an average clock rate.The communications apparatus can include means for receiving, by a UE, asynchronization signal from each of one or more UEs. Further, thecommunications apparatus can include means for performing an averagingprocess to generate an average clock rate based at least on the receivedsynchronization signals. Moreover, the communications apparatus caninclude means for adjusting an internal clock rate based on the averageclock rate.

Another aspect relates to a communications apparatus. The apparatus caninclude a processing system configured to receive a synchronizationsignal from each of one or more UEs. Further, the processing system maybe configured to perform an averaging process to generate an averageclock rate based at least on the received synchronization signals.Moreover, the processing system may further be configured to adjust aninternal clock rate based on the average clock rate.

Still another aspect relates to a computer program product, which canhave a computer-readable medium including code for receiving, by a UE, asynchronization signal from each of one or more UEs. Further, thecomputer-readable medium can include code for performing an averagingprocess to generate an average clock rate based at least on the receivedsynchronization signals. Moreover, the computer-readable medium caninclude code for adjusting an internal clock rate based on the averageclock rate.

According to related aspects, a method enabling distributed frequencysynchronization based on an average clock rate is provided. The methodcan include adjusting an internal clock rate of a UE based on timinginformation provided by a GPS. Further, the method can include selectinga sequence to communicate a synchronization signal transmission from asubset of sequences reserved for GPS connected UEs. Moreover, the methodmay include transmitting the synchronization signal based on theadjusted internal clock rate and selected sequence.

Another aspect relates to a communications apparatus for enablingdistributed frequency synchronization based on an average clock rate.The communications apparatus can include means for adjusting an internalclock rate of a UE based on timing information provided by a GPS.Further, the communications apparatus can include means for selecting asequence to communicate a synchronization signal transmission from asubset of sequences reserved for GPS connected UEs. Moreover, thecommunications apparatus can include means for transmitting thesynchronization signal based on the adjusted internal clock rate andselected sequence.

Another aspect relates to a communications apparatus. The apparatus caninclude a processing system configured to adjust an internal clock rateof a UE based on timing information provided by a GPS. Further, theprocessing system may be configured to select a sequence to communicatea synchronization signal transmission from a subset of sequencesreserved for GPS connected UEs. Moreover, the processing system mayfurther be configured to transmit the synchronization signal based onthe adjusted internal clock rate and selected sequence.

Still another aspect relates to a computer program product, which canhave a computer-readable medium including code for adjusting an internalclock rate of a UE based on timing information provided by a GPS.Further, the computer-readable medium can include code for selecting asequence to communicate a synchronization signal transmission from asubset of sequences reserved for GPS connected UEs. Moreover, thecomputer-readable medium can include code for transmitting thesynchronization signal based on the adjusted internal clock rate andselected sequence.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure inLTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure inLTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control planes.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 is a diagram illustrating a device-to-device communicationsnetwork.

FIG. 8 is a diagram illustrating distributed synchronizationcommunications in a device-to-device communications network.

FIG. 9 is a flow chart of a first method of wireless communication.

FIG. 10 is a flow chart of a second method of wireless communication.

FIG. 11 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus.

FIG. 12 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

FIG. 1 is a diagram illustrating an LTE network architecture 100. TheLTE network architecture 100 may be referred to as an Evolved PacketSystem (EPS) 100. The EPS 100 may include one or more user equipment(UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS)120, and an Operator's IP Services 122. The EPS can interconnect withother access networks, but for simplicity those entities/interfaces arenot shown. As shown, the EPS provides packet-switched services, however,as those skilled in the art will readily appreciate, the variousconcepts presented throughout this disclosure may be extended tonetworks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108.The eNB 106 provides user and control planes protocol terminationstoward the UE 102. The eNB 106 may be connected to the other eNBs 108via a backhaul (e.g., an X2 interface). The eNB 106 may also be referredto as a base station, a base transceiver station, a radio base station,a radio transceiver, a transceiver function, a basic service set (BSS),an extended service set (ESS), or some other suitable terminology. TheeNB 106 provides an access point to the EPC 110 for a UE 102. Examplesof UEs 102 include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a personal digital assistant (PDA), asatellite radio, a global positioning system, a multimedia device, avideo device, a digital audio player (e.g., MP3 player), a camera, agame console, or any other similar functioning device. The UE 102 mayalso be referred to by those skilled in the art as a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

The eNB 106 is connected by an S1 interface to the EPC 110. The EPC 110includes a Mobility Management Entity (MME) 112, other MMEs 114, aServing Gateway 116, and a Packet Data Network (PDN) Gateway 118. TheMME 112 is the control node that processes the signaling between the UE102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theServing Gateway 116, which itself is connected to the PDN Gateway 118.The PDN Gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 is connected to the Operator's IPServices 122. The Operator's IP Services 122 may include the Internet,the Intranet, an IP Multimedia Subsystem (IMS), and a PS StreamingService (PSS).

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNBs 208 may have cellular regions 210 that overlap with oneor more of the cells 202. The lower power class eNB 208 may be a femtocell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radiohead (RRH). The macro eNBs 204 are each assigned to a respective cell202 and are configured to provide an access point to the EPC 110 for allthe UEs 206, 212 in the cells 202. Some of the UEs 212 may be indevice-to-device communication. There is no centralized controller inthis example of an access network 200, but a centralized controller maybe used in alternative configurations. The eNBs 204 are responsible forall radio related functions including radio bearer control, admissioncontrol, mobility control, scheduling, security, and connectivity to theserving gateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplexing (FDD) andtime division duplexing (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSMare described in documents from the 3GPP organization. CDMA2000 and UMBare described in documents from the 3GPP2 organization. The actualwireless communication standard and the multiple access technologyemployed will depend on the specific application and the overall designconstraints imposed on the system.

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames302. Each sub-frame 302 may include two consecutive time slots 304. Aresource grid may be used to represent two time slots, each time slotincluding a resource block (RB) 306. In LTE, the resource grid isdivided into multiple resource elements. Further, in LTE, a RB 306contains 12 consecutive subcarriers in the frequency domain and, for anormal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols inthe time domain, or 84 resource elements. For an extended cyclic prefix,a resource block contains 6 consecutive OFDM symbols in the time domainand has 72 resource elements. A physical DL control channel (PDCCH), aphysical DL shared channel (PDSCH), and other channels may be mapped tothe resource elements.

In LTE-Direct (e.g., D2D communications in an LTE environment),scheduling of D2D communication links may be performed throughdistributed scheduling. In an aspect, request to send (RTS)/clear tosend (CTS) handshake signaling may be performed before each device in aD2D pair attempts to communicate data over a D2D communications link. InLTE-Direct, 24 RBs may be available for RTS/CTS signaling. Further, inLTE-Direct, a RB may be assigned as a RTS block 308 and another RB maybe assigned as a CTS block 310 for each D2D communication link. In otherwords, each D2D communication link may use a RB pair for RTS/CTSsignaling. As used herein, the RB pair may be referred to as aconnection identifier (CID) 312.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource blocks for the UL may be partitioned intoa data section and a control section. The control section may be formedat the two edges of the system bandwidth and may have a configurablesize. The resource blocks in the control section may be assigned to UEsfor transmission of control information. The data section may includeall resource blocks not included in the control section. The UL framestructure results in the data section including contiguous subcarriers,which may allow a single UE to be assigned all of the contiguoussubcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNB. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theeNB. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve UL synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany UL data/signaling. In an aspect, a RACH sequence may be reserved forcommunications of ACK/NACK information from a UE while in idle mode.Each random access preamble occupies a bandwidth corresponding to sixconsecutive resource blocks. The starting frequency is specified by thenetwork. That is, the transmission of the random access preamble isrestricted to certain time and frequency resources. There is nofrequency hopping for the PRACH. The PRACH attempt is carried in asingle subframe (1 ms) or in a sequence of few contiguous subframes anda UE can make only a single PRACH attempt per frame (10 ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for UE 502 and eNB 504 is shown with three layers: Layer 1,Layer 2, and Layer 3. Communication 522 of data/signaling may occurbetween UE 502 and eNB 504 across the three layers. Layer 1 (L1 layer)is the lowest layer and implements various physical layer signalprocessing functions. The L1 layer will be referred to herein as thephysical layer 506. Layer 2 (L2 layer) 508 is above the physical layer506 and is responsible for the link between the UE and eNB over thephysical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB 504and the UE 502. The user plane also includes an internet protocol (IP)sublayer 518 and an application sublayer 520. The IP sublayer 518 andapplication sublayer 520 are responsible for supporting communication ofapplication data between the eNB 504 and the UE 502.

FIG. 6 is a block diagram of a WAN entity (e.g., eNB, MME, etc.) 610 incommunication with a UE 650 in an access network. In the DL, upper layerpackets from the core network are provided to a controller/processor675. The controller/processor 675 implements the functionality of the L2layer. In the DL, the controller/processor 675 provides headercompression, ciphering, packet segmentation and reordering, multiplexingbetween logical and transport channels, and radio resource allocationsto the UE 650 based on various priority metrics. Thecontroller/processor 675 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the UE 650.

The transmit (TX) processor 616 implements various signal processingfunctions for the L1 layer (i.e., physical layer). The signal processingfunctions includes coding and interleaving to facilitate forward errorcorrection (FEC) at the UE 650 and mapping to signal constellationsbased on various modulation schemes (e.g., binary phase-shift keying(BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying(M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded andmodulated symbols are then split into parallel streams. Each stream isthen mapped to an OFDM subcarrier, multiplexed with a reference signal(e.g., pilot) in the time and/or frequency domain, and then combinedtogether using an Inverse Fast Fourier Transform (IFFT) to produce aphysical channel carrying a time domain OFDM symbol stream. The OFDMstream is spatially precoded to produce multiple spatial streams.Channel estimates from a channel estimator 674 may be used to determinethe coding and modulation scheme, as well as for spatial processing. Thechannel estimate may be derived from a reference signal and/or channelcondition feedback transmitted by the UE 650. Each spatial stream isthen provided to a different antenna 620 via a separate transmitter618TX. Each transmitter 618TX modulates an RF carrier with a respectivespatial stream for transmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 656. The RX processor 656 implements various signalprocessing functions of the L1 layer. The RX processor 656 performsspatial processing on the information to recover any spatial streamsdestined for the UE 650. If multiple spatial streams are destined forthe UE 650, they may be combined by the RX processor 656 into a singleOFDM symbol stream. The RX processor 656 then converts the OFDM symbolstream from the time-domain to the frequency domain using a Fast FourierTransform (FFT). The frequency domain signal comprises a separate OFDMsymbol stream for each subcarrier of the OFDM signal. The symbols oneach subcarrier, and the reference signal, is recovered and demodulatedby determining the most likely signal constellation points transmittedby the WAN entity 610. These soft decisions may be based on channelestimates computed by the channel estimator 658. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the WAN entity 610 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the WAN entity 610,the controller/processor 659 implements the L2 layer for the user planeand the control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the WAN entity610. The controller/processor 659 is also responsible for HARQoperations, retransmission of lost packets, and signaling to the WANentity 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the WAN entity 610 may be used by theTX processor 668 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 668 are provided to different antenna 652via separate transmitters 654TX. Each transmitter 654TX modulates an RFcarrier with a respective spatial stream for transmission.

The UL transmission is processed at the WAN entity 610 in a mannersimilar to that described in connection with the receiver function atthe UE 650. Each receiver 618RX receives a signal through its respectiveantenna 620. Each receiver 618RX recovers information modulated onto anRF carrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the controller/processor 675provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

FIG. 7 is a diagram of a device-to-device communications system 700. Thedevice-to-device communications system 700 includes a plurality ofwireless devices 704, 706, 708, 710. The device-to-device communicationssystem 700 may overlap with a cellular communications system, such asfor example, a wireless wide area network (WWAN). Some of the wirelessdevices 704, 706, 708, 710 may communicate together in device-to-devicecommunication using the DL/UL WWAN spectrum, some may communicate withthe base station 702, and some may do both. In another aspect, the WWANmay include multiple base stations (702, 712) that may provide acoordinated communications environment through connectivity provided viaone or more network entities (e.g., MME 714).

For example, as shown in FIG. 7, the wireless devices 708, 710 are indevice-to-device communication and the wireless devices 704, 706 are indevice-to-device communication. The wireless devices 704, 706 are alsocommunicating with the base station 702.

In an operational aspect, the wireless devices (704, 706, 708, 710) maybe synchronized to reduce potential interference and/or collisionswithin the device-to-device communications system 700. In an aspect,synchronization may be enabled through the synchronization informationprovided by a network entity (e.g., MME 714, base station 712). Inanother aspect, synchronization may be performed in a distributed manneramount the wireless devices (704, 706, 708, 710). Further discussion ofdistributed frequency synchronization is provided with reference toFIGS. 8, 9, and 10.

FIG. 8 is a diagram of distributed synchronization communications in adevice-to-device communications network 800. Device-to-devicecommunications network 800 may include multiple UEs (e.g., UEs 802, 804,806, 808), a WAN entity (e.g., eNB, MME, etc.) 816. In an optionalaspect, device-to-device communications network 800 may include a GPSentity 820.

UE 802 may be operable to communication in the device-to-devicecommunications network 800. As part of performing communications in thedevice-to-device communications network 800, the UEs (e.g., 802, 804,806, 808) may perform timing synchronization and/or frequencysynchronization. In an aspect, distributed frequency synchronization maybe performed by UE 802 by receiving synchronization signals (e.g., 812a, 812 b, 812 c) from the other UEs (e.g., 804, 806, 808) in thedevice-to-device communications network 800. UE 802 may process thereceived synchronization signals (e.g., 812 a, 812 b, 812 c) and adjustan internal clock rate based at least in part on the receivedsynchronization signals (e.g., 812 a, 812 b, 812 c). In another aspect,UE 802 may also receive timing information (e.g., 818, 822) from one ormore third parties (e.g., WAN entity 816, GPS entity 820, etc.).Thereafter, UE 802 may transmit a synchronization signal 814 based onthe adjusted internal clock rate.

In an operational aspect, UE 802 may adjust its internal clock rate toalign with the other UEs (e.g., 804, 806, 808) by aligning with anaverage clock rate of the other UEs (e.g., 804, 806, 808). For example,UE 802 may receive synchronization signals (e.g., 812 a, 812 b, 812 c)from a number (3) of other UEs (e.g., 804, 806, 808). Based on at leaston when each synchronization signal was received, UE 802 can determinethe clock rates of each of the other UEs (e.g., 804, 806, 808). FurtherUE 802 may add its internal clock rate to the determined clock rates anddivide the sum by a number of UEs from which the synchronization signalswere received. In another aspect, each of the received synchronizationsignals (e.g., 812 a, 812 b, 812 c) may be received using a sequencefrom a set of sequences. In such an aspect, a sub-set of the set ofsequences may be reserved for UEs that have access to third party (e.g.,GPS) based timing information 822. Further, in such an aspect, where UE802 detects that one of the UEs (e.g., is using a sequence from thereserved sub-set of sequences, then the UE 802 may apply a weightingfactor to that UE (e.g., 804) when performing the summation and divisionprocesses associated with generating an average clock rate.

In another operational aspect in which UE 802 may obtain third party(e.g., GPS entity 820, WAN entity 816) based timing information (822,818), UE 802 may also obtain a set of sequences used for transmission ofthe synchronization signals. In an aspect, the set of sequences mayinclude a sub-set of sequences reserved for UEs (e.g., 802, 804) thatare configured to obtain third party based timing information (e.g.,822, 818). UE 802 may adjust its internal clock rate based on the thirdparty based timing information and may use a sequence selected from thesub-set of sequences for transmission of a synchronization signal 814.

Accordingly, based on the received synchronization signals (e.g., 812 a,812 b, 812 c), and or third party based timing information (818, 822),UE 802 may adjust its internal clock rate to align with the third partytiming information and/or a generated average clock rate.

FIGS. 9 and 10 illustrate various methodologies in accordance withvarious aspects of the presented subject matter. While, for purposes ofsimplicity of explanation, the methodologies are shown and described asa series of acts or sequence steps, it is to be understood andappreciated that the claimed subject matter is not limited by the orderof acts, as some acts may occur in different orders and/or concurrentlywith other acts from that shown and described herein. For example, thoseskilled in the art will understand and appreciate that a methodologycould alternatively be represented as a series of interrelated states orevents, such as in a state diagram. Moreover, not all illustrated actsmay be required to implement a methodology in accordance with theclaimed subject matter. Additionally, it should be further appreciatedthat the methodologies disclosed hereinafter and throughout thisspecification are capable of being stored on an article of manufactureto facilitate transporting and transferring such methodologies tocomputers. The term article of manufacture, as used herein, is intendedto encompass a computer program accessible from any computer-readabledevice, carrier, or media.

FIG. 9 is a flow chart 900 of a first method of wireless communication.The method may be performed by a UE.

In an optional aspect, at block 902, a UE may receive a set of sequencesindicating a sequence used by each of the one or more UEs to transmitthe synchronization signals. In an aspect, the set of sequences mayinclude a subset of sequences reserved for UEs that are connected to aGPS which provides GPS based timing information. In an aspect, thesynchronization signals may be primary synchronization signals (PSS) ina LTE based access network.

At block 904, the UE may receive a synchronization signal from each ofone or more UEs.

At block 906, the UE may perform an averaging process to generate anaverage clock rate based at least on the received synchronizationsignals. In an aspect, as part of the averaging process, the UE maydetermine that at least one of the UEs is using a sequence from thesubset of sequences, and apply a weighting factor to the determinedUE(s). In another aspect, as part of the averaging process, the UE maydetermine a number of UEs from which the synchronization signals werereceived, determine clock rates for each of the one or more UEs based onreception times for each of the synchronization signals, generate aclock rate sum value by adding the determined clock rates together withan internal clock rate, and generate the average clock rate by dividingthe timing sum value by a sum of one plus the number of UEs from whichthe synchronization signals were received. In such an aspect, the UE mayalso determine that a UE is GPS connected, and apply a weighting valueto the GPs connected UE during the averaging processing. Further, the UEmay be determined to be GPS connected based on a sequence used by theGPS connected UE that is within a reserved subset of availablesequences. The weighing value may bias the average clock rate towardsthe GPS connected UE clock rate.

At block 908, the UE may adjust an internal clock rate based on theaverage clock rate. In an aspect, the internal clock rate may beadjusted to align with the average clock rate.

In an optional aspect, at block 910, the UE may select a sequence fortransmission of a synchronization signal by the UE based on the receivedset of sequences. In an aspect, the sequence may be selected to bedifferent than any of the sequences in the set of sequences that is usedby each of the one or more UEs.

At block 912, the UE may transmit a synchronization signal based on theadjusted internal clock rate. In an aspect, the transmission may bebased on a selected sequence.

FIG. 10 is a flow chart 1000 of a second method of wirelesscommunication. The method may be performed by a UE.

In an optional aspect, at block 1002, the UE may receive a set ofsequences indicating sequences used by each of one or more UEs forsynchronization signal transmissions. In an aspect, the set of sequencesmay include a subset of sequences reserved for GPS connected UEs.

At block 1004, the UE may adjust an internal clock rate based on timinginformation provided by a third party. In an aspect, the third partybased timing information may be GPS based timing information. In anotheraspect, the third party may be a WAN entity with which the UEcommunicates (e.g., eNB, MME, etc.).

At block 1006, the UE may select a sequence to communicate asynchronization signal transmission from the subset of sequencesreserved for GPS connected UEs. In an aspect, the UE selects a sequencethat is not used by any of the one or more UEs.

At block 1008, the UE may transmit the synchronization signal based onthe adjusted internal clock rate and selected sequence. In an aspect,synchronization signal is a PSS in a LTE based network.

FIG. 11 is a conceptual data flow diagram 1100 illustrating the dataflow between different modules/means/components in an exemplaryapparatus 1102. The apparatus may be a UE.

The apparatus 1102 includes a reception module 1104 that may receivesynchronization signals 1116 from other UEs (e.g., 804, 806, 808) in aD2D communications system. In an aspect, the synchronization signals maybe transmitted at scheduled times and/or scheduled frequencies to assistUEs in performing distributed synchronization with the D2Dcommunications system. In an optional aspect, reception module 1104 mayfurther receive a set of sequences 1120 indicating a sequence used byeach of the one or more UEs to transmit the synchronization signals. Inanother aspect, reception module 1104 may obtain timing information 1126from a third party. In such an optional aspect, the timing information1126 may be received from a WAN entity (e.g., base station 702, MME714). In another aspect, the timing information 1126 may be receivedfrom a GPS entity (e.g., GPS entity 820). The apparatus 1102 furtherincludes an average clock rate determination module 1106 that mayprocess the received synchronization signals 1116 from the other UEs(e.g., 804, 806, 808) to generate an average clock rate 1118. In anaspect in which the set of sequences 1120 is received and one or moreUEs is using a sequence from within a sub-set reserved for GPS connectedUEs, average clock rate determination module 1106 may apply GPSweighting factor to the GPS connected UEs information during the averageclock rate generation process. The apparatus 1102 further includestransmission sequence module 1110 which may received the set ofsequences 1120 and/or third party timing information 1126. In an aspect,the set of sequences 1120 may include a subset of sequences reserved forUEs that are connected to a global positioning system (GPS) whichprovides GPS based timing information. The apparatus 1102 may furtherinclude internal clock rate adjustment module 1108 that may adjust aninternal clock rate based on the average clock rate 1118. In an aspect,internal clock rate adjustment module 1108 may use a sequence 1122 fortransmission of a synchronization signal 1128. In such an aspect,sequence 1122 may be selected to be different than a sequence used byany other UEs (e.g., 804, 806, 808). The apparatus 1102 may furtherinclude transmission module 1112 that may transmit a synchronizationsignal 1128 based on the adjusted internal clock rate 1124. In anaspect, transmission module 1112 that may transmit a synchronizationsignal 1128 further based on a selected sequence 1122. In anotheroperational aspect, where reception module 1104 received the timinginformation 1126, then internal clock rate adjustment module 1108 mayadjust the internal clock rate based on the received timing information1126. Further, transmission module 1114 may transmit the synchronizationsignal 1128 based on the adjusted internal clock rate 1124 and using asequence 1122 from a sub-set of sequences reserved for GPS connectedUEs.

The apparatus may include additional modules that perform each of thesteps of the algorithm in the aforementioned flow charts of FIGS. 9 and10. As such, each step in the aforementioned flow charts of FIGS. 9 and10 may be performed by a module and the apparatus may include one ormore of those modules. The modules may be one or more hardwarecomponents specifically configured to carry out the statedprocesses/algorithm, implemented by a processor configured to performthe stated processes/algorithm, stored within a computer-readable mediumfor implementation by a processor, or some combination thereof.

FIG. 12 is a diagram 1200 illustrating an example of a hardwareimplementation for an apparatus 1102′ employing a processing system1214. The processing system 1214 may be implemented with a busarchitecture, represented generally by the bus 1224. The bus 1224 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1214 and the overalldesign constraints. The bus 1224 links together various circuitsincluding one or more processors and/or hardware modules, represented bythe processor 1204, the modules 1104, 1106, 1108, 1110, 1112, and thecomputer-readable medium 1206. The bus 1224 may also link various othercircuits such as timing sources, peripherals, voltage regulators, andpower management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1214 may be coupled to a transceiver 1210. Thetransceiver 1210 is coupled to one or more antennas 1220. Thetransceiver 1210 provides a means for communicating with various otherapparatus over a transmission medium. The processing system 1214includes a processor 1204 coupled to a computer-readable medium 1206.The processor 1204 is responsible for general processing, including theexecution of software stored on the computer-readable medium 1206. Thesoftware, when executed by the processor 1204, causes the processingsystem 1214 to perform the various functions described supra for anyparticular apparatus. The computer-readable medium 1206 may also be usedfor storing data that is manipulated by the processor 1204 whenexecuting software. The processing system further includes at least oneof the modules 1104, 1106, 1108, 1110, and 1112. The modules may besoftware modules running in the processor 1204, resident/stored in thecomputer-readable medium 1206, one or more hardware modules coupled tothe processor 1204, or some combination thereof. The processing system1214 may be a component of the UE 650 and may include the memory 660and/or at least one of the TX processor 668, the RX processor 656, andthe controller/processor 659.

In one configuration, the apparatus 1102/1102′ for wirelesscommunication includes means for receiving, by a UE, a synchronizationsignal from each of one or more UEs, means for performing an averagingprocess to generate an average clock rate based at least on the receivedsynchronization signals, and means for adjusting an internal clock ratebased on the average clock rate. In an aspect, the apparatus 1102/1102′may also include means for receiving a set of sequences indicating asequence used by each of the one or more UEs to transmit thesynchronization signals, and means for selecting a sequence fortransmission of a synchronization signal by the UE based on the receivedset of sequences. In an aspect, the apparatus 1102/1202′ means forperforming may be configured to determine that at least one of the oneor more UEs is using a sequence from the subset of sequences, and applya weighting factor to the determined at least one of the one or more UEsas part of the averaging processing. In an aspect, the apparatus1102/1202′ means for performing may be configured to determine a numberof UEs from which the synchronization signals were received, determineclock rates for each of the one or more UEs based on reception times foreach of the synchronization signals, generate a clock rate sum value byadding the determined clock rates together with an internal clock rate,and generate the average clock rate by dividing the timing sum value bya sum of one plus the number of UEs from which the synchronizationsignals were received. In such an aspect, the apparatus 1102/1202′ meansfor performing may be configured to determine that at least one of theone or more UEs is a GPS connected UE, and wherein the weighting valueis applied to the at least one GPS connected UE when the clock rate sumvalue is generated to bias the average clock rate towards a clock rateof the at least one GPS connected UE. In an aspect, the apparatus1102/1102′ may further include means for transmitting a synchronizationsignal based on the adjusted internal clock rate.

In another configuration, the apparatus 1102/1102′ for wirelesscommunication includes means for adjusting an internal clock rate of aUE based on timing information provided by a GPS, means for selecting asequence to communicate a synchronization signal transmission from asubset of sequences reserved for GPS connected UEs, and means fortransmitting the synchronization signal based on the adjusted internalclock rate and selected sequence. In an aspect, the apparatus 1102/1102′may also include means for receiving a set of sequences, including thesubset of sequences, indicating sequences used by each of one or moreUEs for synchronization signal transmissions. In an aspect, theapparatus 1102/1102′ means for selecting may be further configured toselect a sequence that is not used by any of the one or more UEs.

The aforementioned means may be one or more of the aforementionedmodules of the apparatus 1102 and/or the processing system 1214 of theapparatus 1102′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1214 mayinclude the TX Processor 668, the RX Processor 656, and thecontroller/processor 659. As such, in one configuration, theaforementioned means may be the TX Processor 668, the RX Processor 656,and the controller/processor 659 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Further, somesteps may be combined or omitted. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed as a means plus functionunless the element is expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of communications by a user equipment(UE), comprising: receiving a set of sequences indicating a sequenceused by each of one or more UEs to transmit synchronization signals;receiving, by the UE, a synchronization signal from each of the one ormore UEs; performing an averaging process to generate an average clockrate based at least on the received synchronization signals; adjustingan internal clock rate based on the average clock rate; and selecting asecond sequence for transmission of a second synchronization signal bythe UE based on the received set of sequences.
 2. The method of claim 1,wherein the internal clock rate is adjusted to align with the averageclock rate.
 3. The method of claim 1, wherein the second sequence isselected to be different than any of the sequences in the set ofsequences that is used by each of the one or more UEs.
 4. The method ofclaim 1, wherein the set of sequences includes a subset of sequencesreserved for UEs that are connected to a global positioning system (GPS)which provides GPS based timing information.
 5. The method of claim 4,wherein the performing further comprises: determining that at least oneof the one or more UEs is using a sequence from the subset of sequences;and applying a weighting factor to the determined at least one of theone or more UEs as part of the averaging processing.
 6. The method ofclaim 1, wherein the performing further comprises: determining a numberof UEs from which the synchronization signals were received; determiningclock rates for each of the one or more UEs based on reception times foreach of the synchronization signals; generating a clock rate sum valueby adding the determined clock rates together with the internal clockrate; and generating the average clock rate by dividing the clock ratesum value by a sum of one plus the number of UEs from which thesynchronization signals were received.
 7. The method of claim 6, furthercomprising: determining that at least one of the one or more UEs is aGPS connected UE, and wherein a weighting factor is applied to the GPSconnected UE when the clock rate sum value is generated to bias theaverage clock rate towards a clock rate of the GPS connected UE.
 8. Themethod of claim 7, wherein the GPS connected UE is determined based on asequence used by the GPS connected UE that is within a reserved subsetof available sequences.
 9. The method of claim 1, further comprising:transmitting the second synchronization signal based on the adjustedinternal clock rate.
 10. The method of claim 1, wherein thesynchronization signals are primary synchronization signals (PSS) in along term evolution (LTE) based network.
 11. An apparatus forcommunication, the apparatus being a user equipment (UE), comprising:means for receiving a set of sequences indicating a sequence used byeach of one or more UEs to transmit synchronization signals; means forreceiving, by the UE, a synchronization signal from each of the one ormore UEs; means for performing an averaging process to generate anaverage clock rate based at least on the received synchronizationsignals; means for adjusting an internal clock rate based on the averageclock rate: and means for selecting a second sequence for transmissionof a second synchronization signal by the UE based on the received setof sequences.
 12. The apparatus of claim 11, wherein the internal clockrate is adjusted to align with the average clock rate.
 13. The apparatusof claim 11, wherein the second sequence is selected to be differentthan any of the sequences in the set of sequences that is used by eachof the one or more UEs.
 14. The apparatus of claim 11, wherein the setof sequences includes a subset of sequences reserved for UEs that areconnected to a global positioning system (GPS) which provides GPS basedtiming information.
 15. The apparatus of claim 14, wherein the means forperforming is configured to: determine that at least one of the one ormore UEs is using a sequence from the subset of sequences; and apply aweighting factor to the determined at least one of the one or more UEsas part of the averaging processing.
 16. The apparatus of claim 11,wherein the means for performing is configured to: determine a number ofUEs from which the synchronization signals were received; determineclock rates for each of the one or more UEs based on reception times foreach of the synchronization signals; generate a clock rate sum value byadding the determined clock rates together with the internal clock rate;and generate the average clock rate by dividing the clock rate sum valueby a sum of one plus the number of UEs from which the synchronizationsignals were received.
 17. The apparatus of claim 16, wherein the meansfor performing is further configured to: determine that at least one ofthe one or more UEs is a GPS connected UE, and wherein a weightingfactor is applied to the GPS connected UE when the clock rate sum valueis generated to bias the average clock rate towards a clock rate of theGPS connected UE.
 18. The apparatus of claim 17, wherein the GPSconnected UE is determined based on a sequence used by the GPS connectedUE that is within a reserved subset of available sequences.
 19. Theapparatus of claim 11, further comprising: means for transmitting thesecond synchronization signal based on the adjusted internal clock rate.20. The apparatus of claim 11, wherein the synchronization signals areprimary synchronization signals (PSS) in a long term evolution (LTE)based network.
 21. An apparatus for wireless communication, theapparatus being a user equipment (UE), comprising: a processing systemconfigured to: receive a set of sequences indicating a sequence used byeach of one or more UEs to transmit synchronization signals; receive, bythe UE, a synchronization signal from each of the one or more UEs;perform an averaging process to generate an average clock rate based atleast on the received synchronization signals; adjust an internal clockrate based on the average clock rate: and select a second sequence fortransmission of a second synchronization signal by the UE based on thereceived set of sequences.
 22. The apparatus of claim 21, wherein theinternal clock rate is adjusted to align with the average clock rate.23. The apparatus of claim 21, wherein the second sequence is selectedto be different than any of the sequences in the set of sequences thatis used by each of the one or more UEs.
 24. The apparatus of claim 21,wherein the set of sequences includes a subset of sequences reserved forUEs that are connected to a global positioning system (GPS) whichprovides GPS based timing information.
 25. The apparatus of claim 24,wherein the processing system is further configured to: determine thatat least one of the one or more UEs is using a sequence from the subsetof sequences; and apply a weighting factor to the determined at leastone of the one or more UEs as part of the averaging processing.
 26. Theapparatus of claim 21, wherein the processing system is furtherconfigured to: determine a number of UEs from which the synchronizationsignals were received; determine clock rates for each of the one or moreUEs based on reception times for each of the synchronization signals;generate a clock rate sum value by adding the determined clock ratestogether with the internal clock rate; and generate the average clockrate by dividing the clock rate sum value by a sum of one plus thenumber of UEs from which the synchronization signals were received. 27.The apparatus of claim 26, wherein the processing system is furtherconfigured to: determine that at least one of the one or more UEs is aGPS connected UE, and wherein a weighting factor is applied to the GPSconnected UE when the clock rate sum value is generated to bias theaverage clock rate towards a clock rate of the GPS connected UE.
 28. Theapparatus of claim 27, wherein the GPS connected UE is determined basedon a sequence used by the GPS connected UE that is within a reservedsubset of available sequences.
 29. The apparatus of claim 21, whereinthe processing system is further configured to: transmit the secondsynchronization signal based on the adjusted internal clock rate. 30.The apparatus of claim 21, wherein the synchronization signals areprimary synchronization signals (PSS) in a long term evolution (LTE)based network.
 31. A computer program product associated with a userequipment (UE), comprising: a non-transitory computer-readable mediumcomprising code for: receiving a set of sequences indicating a sequenceused by each of one or more UEs to transmit synchronization signals;receiving, by the UE, a synchronization signal from each of the one ormore UEs; performing an averaging process to generate an average clockrate based at least on the received synchronization signals; adjustingan internal clock rate based on the average clock rate: and selecting asecond sequence for transmission of a second synchronization signal bythe UE based on the received set of sequences.
 32. The computer programproduct of claim 31, wherein the internal clock rate is adjusted toalign with the average clock rate.
 33. The computer program product ofclaim 31, wherein the second sequence is selected to be different thanany of the sequences in the set of sequences that is used by each of theone or more UEs.
 34. The computer program product of claim 31, whereinthe set of sequences includes a subset of sequences reserved for UEsthat are connected to a global positioning system (GPS) which providesGPS based timing information.
 35. The computer program product of claim34, further comprising code for: determining that at least one of theone or more UEs is using a sequence from the subset of sequences; andapplying a weighting factor to the determined at least one of the one ormore UEs as part of the averaging processing.
 36. The computer programproduct of claim 31, further comprising code for: determining a numberof UEs from which the synchronization signals were received; determiningclock rates for each of the one or more UEs based on reception times foreach of the synchronization signals; generating a clock rate sum valueby adding the determined clock rates together with the internal clockrate; and generating the average clock rate by dividing the clock ratesum value by a sum of one plus the number of UEs from which thesynchronization signals were received.
 37. The computer program productof claim 36, further comprising code for: determining that at least oneof the one or more UEs is a GPS connected UE, and wherein a weightingfactor is applied to the GPS connected UE when the clock rate sum valueis generated to bias the average clock rate towards a clock rate of theGPS connected UE.
 38. The computer program product of claim 37, whereinthe GPS connected UE is determined based on a sequence used by the GPSconnected UE that is within a reserved subset of available sequences.39. The computer program product of claim 31, further comprising codefor: transmitting the second synchronization signal based on theadjusted internal clock rate.
 40. The computer program product of claim31, wherein the synchronization signals are primary synchronizationsignals (PSS) in a long term evolution (LTE) based network.